So where do we stand going in? Ben Carson is rising dramatically in Iowa – and takes the lead in at least one national poll. Donald Trump, still the national front-runner for the GOP nomination, is pleading with Hawkeye State voters (who cast the first caucus ballots) to back him. Jeb Bush is struggling, and needs a boost tonight.

Another topic that’s almost certain to come up: the U.S. budget deficit. It fell to $439 billion in fiscal 2015, the smallest amount since President Barack Obama took office. But no Republican will applaud that number.

Budget politics will probably feature prominently in the debate tonight, since it’s coming after a House vote on a two-year budget deal that also suspends the U.S. debt ceiling through March 2017. Look for candidates Rand Paul, Ted Cruz and Marco Rubio – all sitting senators – to rip the deal for spending too much money.

In 30 seconds, candidates are asked: What’s your biggest weakness? Kasich goes first but only sort of. He gave a speech instead. Huckabee goes for the joke first but then says he tries to live by the rules. And he turns the question on D.C.: Washington doesn’t play by the rules.

Bush: I can’t fake anger. Trump: I’m too trusting and find it hard to forgive people who deceive me. Carson: not seeing myself as president. Fiorina: I was told I didn’t smile enough after last debate.

OK then. After the weakness question, we’re into policy. Trump is off defending his tax policy and dissing CNBC’s John Harwood at the same time for the way he asked his question. Part of Trump’s tax plan: stamp out “inversions.”

Kasich is whacking Trump for proposing to deport undocumented immigrants. Says we’ve got to have somebody who knows how to do the job. Trump pushes back: “John got lucky with fracking.” And he cites Kasich’s board membership at Lehman Brothers.

“His poll numbers tanked,” Trump says about Kasich. “That’s why he’s on the end.” Kasich denies, though, that he was on the board of Lehman Brothers. But he did work there.

Christie is talking up entitlement reform. I’m the only person who’s got a detailed plan on entitlement reform, he says. He looks right at the camera, too. “The government has lied to you and the government has stolen from you.”

Rubio pivots from a question about his handling of financing to saying he didn’t inherit any money. “I’m not worried about my finances, I’m worried about the financing of everyday Americans,” he continues. Talks up his tax plan, including a child credit.